I've noticed a strange thing: when I highlight a long fragment of a text in the built-in reader by pressing the left key of the mouse and expanding the selected area by dragging the cursor keeping the mouse key pressed, the colour which covers the selected space, disappears for a fraction of a second, and then returns again. It looks like I've been selecting the same fragment twice.

@auster Could you provide a video with this issue? Or a PDF file with instructions how to reproduce what you see.